1. Field of the Invention
This invention generally relates to communication systems and, more particularly, to a system and method for negotiating a link rate in a communication system where link partners are optionally capable of transferring at two or more data rates.
2. Description of the Related Art
FIG. 1 is an auto-negotiation and training state diagram for an IEEE 802.3ap compliant network (prior art). The diagram is a state machine demonstrating the steps in an auto-negotiation (AN) process between boards across a backplane. Devices in such a backplane may be capable of operating at 1 gigabits per second (1 G), 10 G, and both 1 G and 10 G. Further, some units are able to send AN pages, compliant with Clause 73 of 802.3ap, to negotiate a data rate. Following power-up, reset, link fault, or time-out (100) the driver is disabled for a pre-determined period of time, which forces the link partner to restart. Next, the driver sends AN pages and the receiver looks for AN pages (102). If AN pages are detected, then the rate is negotiated based on local and received abilities.
If AN pages are not detected, then the Rx looks for a 1 G signal (104). If a 1 G signal is detected or negotiated, then the data path is configured for 1 G and 1 G acquisition begins (106). If 1 G cannot be detected, the receiver looks for a 10 G signal. If 10 G is negotiated, then the data path is configured for 10 G training and 10 G training begins (110). When 1 G acquisition or 10 G training is complete, the data path is configured for 1 G or 10 G, tracking and data transmission may begin at steps 108 and 112, respectively.
If 100 training does not complete within 500 ms, or if 1 G acquisition does not complete within 50 ms, or if a fault is detected while training, tracking, or acquiring, AN will restart (100).
It would be advantageous if a streamlined process of AN were developed that could account for devices capable of AN, dual-rate devices without AN capacity, and single-rate devices.